An alcoholysis reaction between fat and oil and an alcohol is known as a method of producing a fatty acid ester. This reaction is usually run using an alkali catalyst. There are, besides this reaction, an enzymatic reaction using lipase and a non-catalyst reaction run by bringing an alcohol into contact with fat and oil in a supercritical state or subcritical state. Methods of producing fatty acid esters through such reaction are disclosed in publications JP-A No. 2000-143586, JP-A No. 2001-31991, JP-A No. 2000-109883 and JP-A No. 2000-204392.
Fatty acid esters are generally used as industrial raw material and also have been used as biodiesel fuels in recent years. High purity is required for fatty acid esters used as industrial raw materials or biodiesel fuels. It is pointed out that the total amount of glycerol (total amount of glycerin, monoglyceride, diglyceride and triglyceride) left in a fatty acid ester is a factor that directly affects productivity in industrial applications or a factor that induces engine stains in biodiesel fuel applications (ASTM PS121 Biodiesel for B20).
The reaction between fat and oil and an alcohol not only produces a fatty acid ester but also glycerin. The reaction between fat and oil and an alcohol is considered to be naturally controlled by thermodynamic equilibrium (Oil Chemistry, Vol. 19, No. 8). Therefore, the solubility of glycerin in the fatty acid ester affects the reaction yield, that is, the purity of the fatty acid ester.
To state this reaction in more detail, the reaction is the step-equilibrium reaction of triglyceride which is a major component of fat and oil, the reaction being given by the following reaction formula as described in J. Am. Oil Chem. Soc., 63, pp 1375–1380 (1986).TG+AlcDG+FAEDG+AlcMG+FAEMG+AlcGly+FAE
In the formula, TG represents a triglyceride, DG represents a diglyceride, MG represents a monoglyceride, Alc. represents an alcohol, Gly represents glycerin and FAE represents a fatty acid ester.